The invention relates to a position determination method for a geodetic device.
A multiplicity of methods of measurement has been known since antiquity for recording properties of defined points in a measuring environment, in particular of data having a spatial reference. Standard spatial data recorded are the location of a measuring device in addition to any reference points present, and direction, distance and angle to measuring points. While the position of the geodetic measuring device is known in many applications and measurements are made to unknown positions, there are, however, also applications in which some measuring points are known or are surveyed but the location of the measuring device is unknown.
A generally known example of such surveying devices or geodetic devices is the theodolite or a total station. An overview of geodetic measuring apparatuses of the prior art is provided by “Elektronische Entfernungs—und Richtungsmessung [Electronic Distance and Direction Measuring]” by R. Joeckel and M. Stober, 4th Edition, Verlag Konrad Wittwer, Stuttgart 1999. Such devices have angle and distance measuring functions which permit a direction and distance determination to a selected target. The angle and distance quantities are determined in the internal reference system of the device and optionally must also be linked to an external reference system for an absolute position determination.
In principle, the actual position, i.e. the station coordinates of the measuring device, can be derived as so-called free stationing from measurements to known, fixed measuring points. Free stationing is understood as meaning the determination of the coordinates of a new point from measurements which were made from this new point to surrounding measured, i.e. known measuring points. Such measurements are direction and distance measurements.
First, the position of the surrounding points relative to the station is calculated in a local coordinate system. With the aid of the known coordinates of the surrounding points, adjusted transformation parameters are calculated, if more than the necessary number of measurements are present, from which parameters the coordinates of the new point which are sought then follow. This process can be illustrated by an example: distances and directions are measured to a few surrounding points and the position of these points relative to the location, i.e. in a local coordinate system, is plotted on a transparency. A map of the desired coordinate system is now placed under this transparency. This system may be the national coordinate system or the coordinate system of a specific construction project. The measuring points must now also be found on this map. The transparency is rotated and shifted until the transparency points coincide as well as possible with the points drawn on the map, which can be effected algorithmically by fit calculations by the least squares method. The coordinates of the new point can now be read on the map. This principle is not applied graphically but analytically, it always being necessary to know and to assign the point number of a measuring point and the measured values from the geodetic device to this measuring point.
The calculations required for this purpose are integrated as software in most modern total stations or tacheometers. However, this still means that point numbers and coordinates of the measuring points to which measurements are made must be input in a linked manner; the coordinates of the location and other desired results, such as variances, etc, are then automatically calculated from the measurements and can be stored or output. The minimum number of measurements which are required for such calculation comprise the determination of distance and direction to at least two measuring points. In practice, however, measurements over and above these are, if possible, carried out in order to obtain data on the reliability of the results by overdetermination.
Algorithms with which the location coordinates are calculated from measurements of direction and distance to more than two fixed points may be, for example, similarity transformations associated with a mediating fit, which is also referred to as Helmert transformation in the technical literature.
The erection of a total station and the determination of the actual station coordinates on the basis of known measuring points are generally tailored to the trained surveying engineer with regard to user guidance. The user must reliably identify in the field the measuring points used for calculating the station coordinates and must assign to said measuring points the correct point numbers which establish the link to the position of the measuring point. This is possible as a rule only with a plan in which ground and measuring points are entered. A corresponding manual assignment of actual measurement to measuring point is therefore time-consuming and associated with errors.
Moreover, specific applications, such as, for example, the use of total stations in machine control applications, mean that it is also not necessary for specially trained surveying specialists to operate the devices. Device configurations and user guidance to date are, however, not tailored to this user group.
Position determination methods of the prior art are therefore based on the surveying of known measuring points whose measured values together with the point numbers or the position data of the measuring points are recorded or further processed. This necessary assignment of the measured values to points in the measurement delays the method, increases the susceptibility to errors and complicates the automatability.